Retainer ring and method for polishing a workpiece

ABSTRACT

A chemical mechanical polishing (CMP) machine ( 20 ) includes a workpiece carrier assembly ( 22 ) having a carrier base ( 24 ) with a workpiece contacting side ( 26 ) for holding a first surface ( 30 ) of a workpiece ( 32 ). A method utilizing the CMP machine ( 20 ) to polish the workpiece ( 32 ) and achieve a minimal edge exclusion region ( 92 ) entails adapting the carrier base ( 24 ) to reduce a first diameter ( 53 ) of a workpiece contacting side ( 26 ) of the carrier base ( 24 ) to a second diameter ( 84 ). The method further calls for providing a retainer ring ( 68, 106 ) disposed concentrically on the carrier base ( 24 ) for retaining the workpiece ( 32 ), and applying pressure on the carrier base ( 24 ) to urge a second surface ( 34 ) of the workpiece ( 36 ) against a polishing pad ( 36 ) of the CMP machine ( 20 ). In a first embodiment, the retainer ring ( 68 ) includes a body portion ( 70 ) and a holding lip ( 78 ) protruding radially inward from an inner periphery ( 80 ) of the body portion ( 70 ) and overlying an outer edge of the workpiece ( 32 ) to reduce the first diameter ( 53 ) of the workpiece contacting side ( 26 ) to the second diameter ( 84 ). In an alternative embodiment, the carrier base ( 24 ) is modified to reduce the first diameter ( 53 ) of the workpiece contacting side to the second diameter ( 84 ). Correspondingly, a width of the retainer ring  106  is defined to include a value substantially equivalent to one half of the difference between the first diameter ( 53 ) and the second diameter ( 84 ).

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of chemical mechanicalpolishing machines. More specifically, the present invention relates toa method and apparatus for polishing a semiconductor wafer to obtain aminimal edge exclusion.

BACKGROUND OF THE INVENTION

[0002] The production of integrated circuits begins with the creation ofhigh quality semiconductor wafers. The semiconductor wafers aretypically polished prior to integrated circuit fabrication so that aflat surface is available upon which the circuit fabrication can takeplace. Additionally, during the integrated circuit fabrication process,layers of, for example, conductors and dielectrics, are built up on thewafer, on top of which other such layers are to be created. Thus, it istypically necessary to “re-flatten” the wafer surface during the actualfabrication of the integrated circuit and not merely before it. The actof re-flattening is referred to as planarization.

[0003] Chemical mechanical polishing (CMP) is a process for improvingthe surface planarity of a semiconductor wafer and involves the use ofmechanical pad polishing systems usually with a silica-based slurry. CMPgenerally includes attaching one side of the wafer to a flat surface ofa wafer carrier or chuck and pressing the wafer against a flat polishingsurface. The polishing surface is moved under the wafer, and the wafermay also be rotated about its vertical axis and oscillated back andforth to improve polishing action. The polishing surface is generally apad attached to a rigid flat table which is rotated to provide movementand onto which an abrasive and/or chemical slurry is pumped. The jointfunctions of the pad, the slurry, and the relative movements of thecomponents produce a combined chemical and mechanical process at thewafer surface which produces a highly flat surface on a wafer wheresurface variations are kept to less than, for example, 0.5 μm.

[0004] However, prior art CMP systems for planarizing semiconductorwafers have a limitation related to polishing uniformity known as “edgeexclusion.” Edge exclusion occurs when too much of the exposed surfaceof the semiconductor wafer surface is polished. This causes the edge orouter portion of the wafer to be unusable for integrated circuitfabrication. Thus, the larger the edge exclusion on the semiconductorwafer, the lower the number of integrated circuits that a fabricationfacility can produce per wafer. For example, prior art CMP systemstypically produce an edge exclusion of approximately six millimeterswide on an eight inch (i.e., 203.2 mm) diameter wafer. This sixmillimeter edge exclusion represents an approximate eleven and a halfpercent reduction of surface area of a wafer that may be used forintegrated circuit fabrication.

[0005] Given semiconductor processing costs, it is quite possible that asingle eight inch partially processed wafer is worth $10,000 or more inUnited States currency when planarization is performed. Accordingly, thehigh cost of complex semiconductor wafers combined with a highlycompetitive market has driven the need for a reduction in the size ofthe edge exclusion in order to maximize the number of integratedcircuits that may be fabricated on a single wafer.

[0006] In an attempt to respond to this need, original equipmentmanufacturers (OEMs) are manufacturing CMP systems that now yield anedge exclusion of approximately three millimeters. Thus, on an eightinch wafer, this represents nearly a six and a half percent increase inuseable surface area over wafers polished using CMP systems producing asix millimeter edge extension. These newly designed CMP systems may costin the range of two to three million dollars. For those fabricationfacilities that have significant capital to invest, the purchase of anew CMP system may be acceptable. However, for those fabricationfacilities in which financial resources may not be so readily availableor for those that already own a CMP system, the investment of a new CMPsystem may be quite objectionable.

[0007] Other OEMs and second source manufacturers have attempted toretrofit existing CMP systems in order to yield the desired threemillimeter edge exclusion. Such retrofits involve software and hardwareconfiguration changes that involve the replacement of, for example, thewafer carrier assembly of a CMP system, the inclusion of a variablepressurized retaining ring and corresponding software processes,redesigned polishing pads, and so forth. Such aftermarket parts aretypically not part of an OEM's core business. Hence, this createsproblems for the OEMs in terms of investment of time and effort inengineering and producing these aftermarket products. Moreover, thedevelopment cost of new components and software is typically passed tothe consumer, i.e., the fabrication facilities that purchase theretrofit components for their existing CMP systems. While thisinvestment may not be as great as purchasing a new CMP system, thesemodifications to existing equipment can still cost in the range offifteen to seventy thousand dollars when installed. Again, such costsmay be objectionable to some fabrication facilities.

SUMMARY OF THE INVENTION

[0008] Accordingly, it is an advantage of the present invention that animproved retainer ring for a wafer carrier assembly and a method forpolishing a workpiece utilizing an existing polishing machine areprovided.

[0009] It is another advantage of the present invention that it limitsedge exclusion compared to that which occurs on a semiconductor waferpolished by known processes.

[0010] Yet another advantage of the present invention is that it forms asimple modification to existing wafer carrier assemblies and through themodification improves the CMP process for semiconductor wafers.

[0011] The above and other advantages of the present invention arecarried out in one form by a retainer ring for retaining a workpiecewithin a workpiece carrier assembly of a polishing machine. Theworkpiece carrier assembly includes a carrier base for holding a firstsurface of the workpiece and for abutting a second surface, opposite thefirst surface, of the workpiece against a polishing pad of the polishingmachine. The retainer ring comprises a body portion configured to bedisposed concentrically on an outer periphery of the carrier base and aholding lip for retaining the workpiece, the holding lip protrudingradially inward from an inner periphery of the body portion.

[0012] The above and other advantages of the present invention arecarried out in another form by a method for utilizing a polishingmachine to polish a workpiece having a minimal edge exclusion region.The polishing machine includes a workpiece carrier assembly having acarrier base with a workpiece contacting side for holding a firstsurface of the workpiece. The workpiece contacting side of the carrierbase exhibits a first diameter. The method calls for adapting thecarrier base to reduce the first diameter of the workpiece contactingside to a second diameter and providing a retainer ring disposedconcentrically on an outer periphery of the carrier base for retainingthe workpiece when the workpiece is held by the carrier base. The methodfurther calls for applying pressure on an upper side, opposite from theworkpiece contacting side, of the carrier base to urge a second surfaceof the workpiece into sliding engagement with a polishing pad of thepolishing machine.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] A more complete understanding of the present invention may bederived by referring to the detailed description and claims whenconsidered in connection with the Figures, wherein like referencenumbers refer to similar items throughout the Figures, and:

[0014]FIG. 1 shows a partial block diagram of a chemical mechanicalpolishing (CMP) machine that may use the preferred embodiment of thepresent invention;

[0015]FIG. 2 shows a bottom view of a semiconductor wafer surrounded byan existing retainer ring attached to a carrier base of the CMP machineof FIG. 1;

[0016]FIG. 3 shows a perspective view of a retainer ring in accordancewith a preferred embodiment of the present invention;

[0017]FIG. 4 shows a cross-sectional side view of a workpiece carrierassembly of the CMP machine of FIG. 1 with the retainer ring of FIG. 3;

[0018]FIG. 5 shows a semiconductor wafer polished in accordance with apreferred embodiment of the present invention; and

[0019]FIG. 6 shows a cross-sectional side view of a workpiece carrierassembly of the CMP machine of FIG. 1 with a carrier base and a retainerring in accordance with an alternative embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020]FIG. 1 shows a partial block diagram of a chemical mechanicalpolishing (CMP) machine 20 that may use the preferred embodiment of thepresent invention. CMP machine 20 generally includes a workpiece carrierassembly 22 having a carrier base 24 with a workpiece contacting side 26and an upper side 28, opposite from workpiece contacting side 26.Workpiece contacting side 26 is configured to hold a first surface 30 ofa workpiece, or semiconductor wafer 32. Workpiece carrier assembly 22picks up semiconductor wafer 32 by a vacuum force and places a secondsurface 34, opposite first surface 30, of wafer 32 in contact with apolishing pad 36 supported by a platen 38. Slurry 40 is applied topolishing pad 36.

[0021] Pressure, as represented by an arrow 42, is applied on upper side28 of carrier base 24 so that semiconductor wafer 32 contacts polishingpad 36. Rotation of carrier assembly 22, as represented by a secondarrow 43, urges second surface 34 of semiconductor wafer 32 in slidingengagement with polishing pad 36 so that semiconductor wafer 32 isconditioned in the CMP process.

[0022] CMP machine 20 represents a conventional chemical mechanicalpolishing system. Hence, those skilled in the art will recognize thatCMP machine 20 may include features such as a user interface, input andoutput elements for supplying and receiving semiconductor wafers,multiple workpiece carrier assemblies, necessary cabinets and accesspanels for the mechanical and electrical components within machine 20,and so forth (not shown) and will not be discussed in detail herein.Software programs resident in computer memory of CMP machine 20 functionto control the downward pressure on semiconductor wafer 32, therotational speed of carrier assembly 22, the application of slurry 40 onpolishing pad 36, and so forth.

[0023] In addition, CMP machine 20 is shown using rotary motion torotate semiconductor wafer 32 relative to polishing pad 36 for clarityof illustration. However, it should be understood to those skilled inthe art that CMP machine 20 may use a combination of rotational andorbital motion, or rotational and linear motion. That is, carrierassembly 22 may rotate in a circular path, while polishing pad 36rotates in an orbital path. Alternatively, carrier assembly 22 mayrotate in a circular path, while polishing pad 36 moves in a linearpath.

[0024]FIG. 2 shows a bottom view of semiconductor wafer 32 surrounded byan existing retainer ring 44 attached to carrier base 24 of CMP machine20 of FIG. 1. Retainer ring 44 was not shown in FIG. 1 so thatsemiconductor wafer 32 would be viewable between carrier base 24 andpolishing pad 36. However, CMP machine 20 typically includes retainerring 44 which functions to retain wafer 32 within a pocket of workpiececarrier assembly 22 (FIG. 1) formed by workpiece contacting side 26 andan inner periphery 48 of retainer ring 44.

[0025]FIG. 2 further shows semiconductor wafer 32 having an edgeexclusion region 50 about a perimeter 52 of wafer 32 that forms in theconventional CMP process. Wafer 32 floats within the pocket formed byworkpiece contacting side 26 and inner periphery 48 of retainer ring 44.Workpiece contacting side 26 exhibits a first diameter 53, defined byinner periphery 48, that is greater than a diameter 55 of wafer 32.Accordingly, when pressure 42 (FIG. 1) is applied on upper side 28(FIG. 1) of carrier base 24 (FIG. 1) so that wafer 32 contacts polishingpad 36 (FIG. 1), polishing pad 36 may be forced into a gap 54 betweeninner periphery 48 of retainer ring 44 and perimeter 52 of wafer 32.Consequently, excessive polishing of semiconductor wafer 32 occurs aboutperimeter 52 to form edge exclusion region 50.

[0026] Edge exclusion region 50 is defined by a width 57. Width 57 ofedge exclusion region 50 significantly affects the ability to includeintegrated circuits on semiconductor wafer 32. For example, anintegrated circuit pattern 56 is formed on second surface 34 ofsemiconductor wafer 32. As can be seen, in integrated circuit pattern56, integrated circuits 58, 60, 62 and 64 cannot be used because theyfall, at least in part, within edge exclusion region 50. Thus, edgeexclusion region 50 forms an area on second surface 34 of wafer 32 whichexcludes the acceptable fabrication of integrated circuits. Width 57 ofedge exclusion region 50 typically ranges from 5 to 7 mm.

[0027] The present invention limits width 57 of edge exclusion region 50when polishing wafer 32 utilizing CMP machine 20 compared to that whichoccurs on a semiconductor wafer polished by known processes. Inparticular, width 57 of edge exclusion region 50 is decreased from 5 to7 mm on an eight inch (i.e. 203.2 mm) diameter wafer to approximately 3mm. Width 57 of edge exclusion region 50 is decreased by adaptingcarrier base 24 to reduce first diameter 53 of workpiece contacting side24, thus decreasing gap 54 and allowing less space in which wafer 32 mayfloat and in which polishing pad 36 may be forced.

[0028] Referring to FIGS. 3 and 4, FIG. 3 shows a perspective view of aretainer ring 68 in accordance with a preferred embodiment of thepresent invention. FIG. 4 shows a cross-sectional side view of workpiececarrier assembly 22 of CMP machine 20 (FIG. 1) with retainer ring 68.Retainer ring 68 is provided to replace existing retainer ring 44 (FIG.2) of workpiece carrier assembly 22 and functions to retain wafer 32within workpiece carrier assembly 22 of CMP machine 20 (FIG. 1).

[0029] Retainer ring 68 includes a body portion 70 configured to bedisposed concentrically on an outer periphery 72 of carrier base 24 ofworkpiece carrier assembly 22. Body portion 70 includes threaded holes74, and bolts 76 couple retainer ring 68 to carrier base 24.

[0030] Retainer ring 68 further includes a holding lip 78 protrudingradially inward from an inner periphery 80 of body portion 70. A width79 of holding lip 78 is shown greatly exaggerated in FIG. 4 for clarityof illustration. However, retainer ring 68 is manufactured such thatwidth 79 of holding lip 78 is in a range of 0.005 to 0.012 inches (0.127to 0.3048 mm). For example, for a CMP machine, such as CMP machine 20,configured to polish semiconductor wafer 32 having diameter 55 (FIG. 2)of eight inches (203.2 mm), holding lip 78 may protrude radially inwardsubstantially 0.010 inches (0.254 mm) from inner periphery 80.

[0031] When retainer ring 68 is coupled to carrier base 24, retainerring 68 is positioned such that holding lip 78 overlies an outer edge 82of workpiece contacting side 26 of carrier base 24 to reduce firstdiameter 53 of workpiece contacting side 26 to a second diameter 84. Byway of example when width 79 of holding lip 78 is substantially 0.010inches, second diameter 84 is reduced substantially 0.020 inches fromfirst diameter 53. Thus, when wafer 32 is held in workpiece carrierassembly 22, holding lip 78 approaches perimeter 52 of wafer 32 and agap 86 formed between wafer 32 and inner periphery 80 of body portion 70is minimized.

[0032] Holding lip 78 exhibits a height 88 configured to accommodate thethickness of wafer 32. Thus, like retainer ring 44, retainer ring 68functions to retain wafer 32 within a pocket 90 of workpiece carrierassembly 22 formed by workpiece contacting side 26 and holding lip 78 ofretainer ring 68 when wafer 32 is held by carrier base 24.

[0033] In a preferred embodiment, retainer ring 68 is readily machinedfrom polyphenyl sulfide (PPS). PPS may be unmodified or modified withmodifiers such as Teflon® PTFE (Polytetrafluoroethylene), MoS(Molybdenum disulfide), graphite, and so forth. PPS is rigid, hard, andresistant to corrosion. Alternatively, retainer ring 68 may befabricated from Delrin® also characterized by strength, stiffness,hardness, and solvent and fuel resistance. Retainer ring 68 is precisionmachined to achieve tolerances of +/− one micron for holding lip 78.

[0034]FIG. 5 shows semiconductor wafer 32 polished in accordance with apreferred embodiment of the present invention and having an edgeexclusion region 92. It has been discovered that the replacement ofexisting retainer ring 44 (FIG. 2) with retainer ring 68 in workpiececarrier assembly 22 results in edge exclusion region 92 having a width93 of approximately 3 mm being formed on wafer 32 during the chemicalmechanical polishing process utilizing CMP machine 20. Edge exclusionregion 92 with width 93 of 3 mm represents a minimal edge exclusioncurrently achievable on newly designed CMP machines and CMP machineswith redesigned workpiece carrier assemblies.

[0035] Width 93 of edge exclusion region 92 represents nearly a fiftypercent reduction of edge exclusion region 92 over edge exclusion region50 (FIG. 2) formed during a conventional CMP process using retainer ring44 (FIG. 2). This reduction of the edge exclusion nets an approximate6.4% increase in usable surface area of semiconductor wafer 32 over edgeexclusion region 50. As such, an integrated circuit pattern 94, havingthe same surface area as integrated circuit pattern 56 of FIG. 2,includes integrated circuits 96, 98, 100, and 102. By minimizing edgeexclusion region 92 on semiconductor wafer 32, the yield of integratedcircuits from wafer 32 increases.

[0036] Moreover, the replacement of retainer ring 44 with retainer ring68 on workpiece carrier assembly 22 is far less costly than replacementof the entire workpiece carrier assembly on an existing CMP machine, orpurchase of an entirely new CMP machine. For example, through its simplemanufacture and retrofit onto the existing carrier base 24 (FIG. 3),retainer ring 68 results in significant savings for the consumer interms of time and effort in testing and qualifying replacement carrierassemblies or purchasing a replacement CMP machine. Thus, retainer ring68 may be one to three hundredths of the cost of a replacement carrierassembly or one thousandth of the cost of a replacement CMP machine.

[0037]FIG. 6 shows a cross-sectional side view of workpiece carrierassembly 22 of the CMP machine of FIG. 1 with a carrier base 104 and aretainer ring 106 in accordance with an alternative embodiment of thepresent invention. Carrier base 104 may be a replacement unit forcarrier base 24 (FIG. 4). As such, carrier base 104 and retainer ring106 may form a retrofit kit that may be used to upgrade an existing CMPmachine to polish wafers to achieve edge exclusion region 92 with width93 (FIG. 5) of 3 mm rather than edge exclusion region 50 (FIG. 2) withwidth 57 (FIG. 2) of 6 mm. Alternatively, carrier base 104 may beadapted from carrier base 24 by precision machining the existing carrierbase 24. In either case, carrier base 104 has a workpiece contactingside 108 exhibiting second diameter 84 that is reduced from firstdiameter 53 (FIG. 2) by a value in a range of 0.010 to 0.024 inches(0.254 to 0.6096 mm).

[0038] Retainer ring 106 is provided to replace retainer ring 44 (FIG.2). That is, retainer ring 106 is disposed concentrically on an outerperiphery 112 of carrier base 104 and serves to retain semiconductorwafer 32 when wafer 32 is held by carrier base 104. A width 114 ofretainer ring 106 is defined to include a value substantially equivalentto a one half of a difference between first diameter 53 and seconddiameter 84. By way of example, when second diameter 84 is reduced fromdiameter 53 by a total of 0.020 inches, width 114 is a sum of a width(not shown) of retainer ring 44 and 0.010 inches.

[0039] The reduction of second diameter 84 from first diameter 53, andthe corresponding increase of width 114 of retainer ring 106 relative toretainer ring 44, achieves a decrease in a gap 116 between retainer ring106 and perimeter 52 of wafer 32 relative to gap 54 (FIG. 2). As such,edge exclusion region 92 (FIG. 5) with width 93 of 3 mm is produced.

[0040] The replacement of carrier base 24 with carrier base 104, oralternatively, adaptation of carrier base 24 to produce carrier base104, and the replacement of retainer ring 44 with retainer ring 106,achieves significant cost savings over the replacement of workpiececarrier assembly 22 or the replacement of CMP machine 20.

[0041] In summary, the present invention teaches of an improved retainerring for a wafer carrier assembly and a method for polishing a workpieceusing an existing chemical mechanical polishing machine. By decreasingthe amount of gap between the perimeter of a semiconductor wafer and aretainer ring, when the wafer is positioned in a carrier base of aworkpiece carrier, the edge exclusion region is reduced by nearly fiftypercent over that which occurs on a semiconductor wafer polished bypreviously known chemical mechanical polishing processes. In addition,the retainer ring and the adaptation of the carrier base to reduce thediameter of the workpiece contacting side of the carrier base form asimple and cost effective modification to existing wafer carrierassemblies and through the modification improves the CMP process forsemiconductor wafers.

[0042] Although the preferred embodiments of the invention have beenillustrated and described in detail, it will be readily apparent tothose skilled in the art that various modifications may be made thereinwithout departing from the spirit of the invention or from the scope ofthe appended claims. For example, the teachings of the present inventionmay be adapted to successfully achieve minimal edge exclusion regions onworkpieces of different diameters and manufactured from a variety ofmaterials. In addition, the teachings of the present invention art notlimited to existing CMP machines but may be adapted for use with new CMPmachines to achieve minimal edge exclusion regions on workpieces.

What is claimed is:
 1. A retainer ring for retaining a workpiece withina workpiece carrier assembly of a polishing machine, said workpiececarrier assembly including a carrier base for holding a first surface ofsaid workpiece and for abutting a second surface, opposite said firstsurface, of said workpiece against a polishing pad of said polishingmachine, said retainer ring comprising: a body portion configured to bedisposed concentrically on an outer periphery of said carrier base; anda holding lip for retaining said workpiece, said holding lip protrudingradially inward from an inner periphery of said body portion.
 2. Aretainer ring as claimed in claim 1 wherein said body portion isconfigured to be coupled to said carrier base.
 3. A retainer ring asclaimed in claim 1 wherein when said workpiece is held in said carrierbase, said holding lip is configured to approach a perimeter of saidworkpiece to minimize a gap between said holding lip and said perimeter.4. A retainer ring as claimed in claim 1 wherein said holding lipexhibits a width, said width protruding radially inward, and said widthbeing in a range of 0.005 and 0.012 inches.
 5. A retainer ring asclaimed in claim 4 wherein said width of said holding lip issubstantially 0.010 inches.
 6. A retainer ring as claimed in claim 1wherein said carrier base includes a workpiece contacting side having afirst diameter, and said holding lip is configured to overlie an outeredge of said workpiece contacting side of said carrier base to reducesaid first diameter of said workpiece contacting side to a seconddiameter.
 7. A retainer ring as claimed in claim 1 wherein said holdinglip exhibits a height configured to accommodate a thickness of saidworkpiece.
 8. A retainer ring as claimed in claim 1 wherein saidretainer ring is adapted to replace an existing retainer ring of saidworkpiece carrier assembly.
 9. A method for utilizing a polishingmachine to polish a workpiece to achieve a minimal edge exclusionregion, said polishing machine including a workpiece carrier assemblyhaving a carrier base with a workpiece contacting side for holding afirst surface of said workpiece, said workpiece contacting sideexhibiting a first diameter, and said method comprising: adapting saidcarrier base to reduce said first diameter of said workpiece contactingside to a second diameter; providing a retainer ring disposedconcentrically on an outer periphery of said carrier base for retainingsaid workpiece when said workpiece is held by said carrier base; andapplying pressure on an upper side, opposite from said workpiececontacting side, of said carrier base to urge a second surface of saidworkpiece into sliding engagement with a polishing pad of said polishingmachine.
 10. A method as claimed in claim 9 wherein said carrier base isan existing carrier base exhibiting said first diameter, and saidadapting operation includes modifying said existing carrier base toreduce said first diameter of said workpiece contacting side to obtainsaid second diameter.
 11. A method as claimed in claim 10 wherein saidproviding operation comprises defining a width of said retainer ring toinclude a value substantially equivalent to one half of a differencebetween said first diameter and said second diameter.
 12. A method asclaimed in claim 11 wherein said value is in a range of 0.005 to 0.012inches.
 13. A method as claimed in claim 9 wherein said carrier base isan existing carrier base exhibiting said first diameter, and saidproviding operation includes: producing said retainer ring having a bodyportion and a holding lip protruding radially inward from an innerperiphery of said body portion, said body portion being configured to bedisposed concentrically on said outer periphery of said carrier base;and positioning said retaining ring such that said holding lip overliesan outer edge of said workpiece contacting side of said carrier base toreduce said first diameter of said workpiece contacting side to obtainsaid second diameter.
 14. A method as claimed in claim 13 wherein saidproducing operation includes establishing a width of said holding lip tobe substantially equivalent to one half of a difference between saidfirst diameter and said second diameter.
 15. A method as claimed inclaim 14 wherein said width of said holding lip is in a range of 0.005to 0.012 inches.
 16. A workpiece carrier assembly retrofit kit foradapting a workpiece carrier assembly of a polishing machine to polish aworkpiece having a minimal edge exclusion region, said workpiece carrierassembly including an existing carrier base and an existing retainerring coupled to said existing carrier base, said existing carrier basehaving a workpiece contacting side exhibiting a first diameter, saidexisting retainer ring exhibiting a first width, and said kitcomprising: a carrier base configured to replace said existing carrierbase, said carrier base having a workpiece contacting side exhibiting asecond diameter, said second diameter being less than said firstdiameter of said existing carrier base; and a retaining ring configuredto couple to said carrier base, said retaining ring exhibiting a secondwidth, said second width being substantially equivalent to a sum of saidfirst width and a value substantially equivalent to one half of adifference between said first diameter and said second diameter.